dpkg -l | grep ruby
ii  libruby2.1:amd64                   2.1.5-2+deb8u3                    amd64        Libraries necessary to run Ruby 2.1
ii  ruby                               1:2.1.5+deb8u2                    all          Interpreter of object-oriented scripting language Ruby (default version)
ii  ruby-dev                           1:2.1.5+deb8u2                    all          Header files for compiling extension modules for Ruby (default version)
ii  ruby-passenger                     4.0.53-1                          amd64        Rails and Rack support
ii  ruby-rack                          1.5.2-3+deb8u1                    all          Modular Ruby webserver interface
ii  ruby-zip                           1.1.6-1                           amd64        Ruby module for reading and writing zip files
ii  ruby2.1                            2.1.5-2+deb8u3                    amd64        Interpreter of object-oriented scripting language Ruby
ii  ruby2.1-dev:amd64                  2.1.5-2+deb8u3                    amd64        Header files for compiling extension modules for the Ruby 2.1
ii  rubygems-integration               1.8                               all          integration of Debian Ruby packages with Rubygems